The present invention is generally related to a drilling electric discharge machine, and more particularly, to an automatic breakthrough detection device for drilling electric discharge machine.
During the operation of a drilling electric discharge machine, an operator is required to observe the spraying effect from the drilling to determine if the process has finished and furthermore the operator is also required to manually adjust the machine table for the next drilling after every cycle. Recent computer numerically controlled (CNC) drilling electric discharge machines deploy a system for entering the drilling depth and the electrode wear compensation value before performing the drilling process. If any process variable deviations exist such as electrode discharge bias, water pressure fluctuation or deficiency, or water impurity, the electric discharge will become unsteady. Consequently the fluctuation in the electric discharge will increase the wear of the electrode and furthermore decrease the processing rate. If the electrode wear is too fast, the system might automatically terminate itself before drilling is finished. Occasionally if the electric discharge suddenly increases at breakthrough, the diameter of the hole will be affected causing non-linearity in the overall diameter.
Prior art U.S. Pat. No. 4,767,903 teaches the use of a conductivity measuring plate under a workpiece for detecting the breakthrough when the electrode makes contact with the conductivity measuring plate. This method however is limited to use only with workpiece that has a flat bottom surface and cannot be used on curved surfaces. Furthermore the conductivity measuring plate has only a limited life span. Another prior art U.S. Pat. No. 4,484,051 teaches a method by dividing the process factors into main factor such as servo voltage difference, and assisting factors such as water pressure, flow, electrode movement speed, and direction deviations to determine if drilling is finished. However this method requires a complicated system setup because the detection of pressure and process flow is not easy and the sensors for detection are expensive which are the shortcomings of this method.
The present invention solves the shortcoming of the above-mentioned conventional drilling electric discharge machines by reducing the process time and electrode wear. The automatic breakthrough detection device and method thereof for use with drilling electric discharge machine utilizes the facts of the variation of high frequency spectrum components of the provided discharge voltage and the variation of servo-feed-rate of the electrode.
An object of the present invention is to provide an automatic breakthrough detection device for use with drilling electric discharge machines and method thereof which is simple, provides real-time adjustment of process factors, and is applicable to any curved surfaces.
Another object of the present invention is to provide an automatic breakthrough detection device for use with drilling electric discharge machines and method thereof which reduces process time and electrode wear.
In one embodiment of the present invention, the automatic breakthrough detection device for use with drilling electric discharge machines comprises: a high frequency spectrum detecting analyzer and a breakthrough judging logic device. The high frequency spectrum detecting analyzer detects the variations of the high frequency spectrum components during the drilling electric discharge and processes the data to generate a digital logic determining signal which can determine whether breakthrough has occurred or not. The breakthrough judging logic device receives the digital logic determining signal sent out from the high frequency spectrum detecting analyzer to determine if the drilling breakthrough has occurred and sends out a result determining signal. The drilling electric discharge machine can automatically adjust the electric discharge parameter according to the result determining signal or automatically retract the electrode and move on to the next drilling process.
In another embodiment of the present invention, the high frequency spectrum detecting analyzer performs analysis on the resonance frequency of the discharge voltage after rectification and filtration to generate a digital logic determining signal which determines if the drilling breakthrough has occurred. The breakthrough judging logic device judges the digital logic determining signal to indicate the status of the drilling by comparing the feed rate and the actual downward movement of the electrode. The final result is determined after a few repetitions are performed for verification purposes. After confirming the completion of drilling, the breakthrough judging logic device sends out a signal to adjust the electric discharge parameter of the drilling electric discharge machine such as to decrease the amount of electric discharge to ensure steady electrode operation so as to end the drilling process. If there are other drilling processes required at the time, the machine will continue to perform the other drilling process.